Field of the Invention
The invention relates to the textile industry, and more particularly it relates to loopers incorporated in machines for sewing-up webs of netting.
Description of the Prior Art
There is known a looper to a machine for sewing-up netting webs, including a knee-shaped needle operatively connected with the main shaft of the machine, mounted on a vertical bar of the machine overlying the device for guiding the webs of netting towards the needle, and carrying the needle thread.
The knee-shaped needle includes a stud and a blade with a passage and the eye of the needle, interconnected by a bend or crosspiece (cf. SU Inventor's Certificate No. 820 292, published in "Discoveries. Inventions" Bulletin No. 28 on July 30, 1983).
In machines of this kind the looper in the form of a knee-shaped needle carrying the first looping thread interacts with a working needle carrying the needle thread and with a hook-shaped looper driven through a complex three-dimensional motion and carrying the second looping thread.
When the loop formed by the second looping thread is engaged, the blade of the knee-shaped needle enters the path of the hook which at this moment commences its motion from the rear dead centre in the direction of the working stroke of the needle, and sheds the loops formed of the needle thread and the first looping thread. So as to avoid being engaged by the blade of the needle driven through its working stroke, i.e. moving downwardly, and thus to prevent a breakdown, the hook brought close to the needle instantly turns about the longitudinal axis of the bar carrying it, as the needle takes the loop formed of the second looping thread, for the tip of the hook to clear the path of the needle in due time before their encounter, and thus to bypass the needle. This instant motion is controlled by the appropriate stationary cam of the machine interacting with a spring-urged pivoted arm of the bar carrying the looper hook. As the main shaft of the machine attains a corresponding angular speed, the follower on the pivoted arm of the bar carrying the looper hook, while rolling down the slope of the cam toward its centre, alternatingly clears (rises off) the cam and then strikes it under the action of the spring, causing excessive noise and vibration of the machine, and also interfering with loop formation. To abate the noise and vibration and to improve the conditions of the taking of the loop of the second looping thread by the needle, the rotational speed of the main shaft is reduced, i.e. the sewing speed is slowed down. In this arrangement it is impossible to make the control cam less steep, i.e. to make its grade smoother and thus to enhance the dynamics of the machine performance and provide for a higher sewing speed, since this would lead to inadvertent engagement between the looper hook and the needle, which amounts to a breakdown. If, on the other hand, the looper hook is moved aside from the needle path somewhat earlier, the blade of the needle would not enter the loop of the second looping thread, and a stitch would not be made. As the loop of the second looping thread is cast off the blade of the needle, its runs extend all but perpendicularly to the blade with its tip and the needle eye, so that the loop is caught by the tip of the needle blade, the loop-shedding is delayed, and the runs of the loop are overextended, which affects the stitch-forming process, and the shedding of the loop is accompanied by a specific snap causing additional vibration of the loopers and thus interfering with a normal looping operation.
In the construction of the prior art the looper needle is fixed on the reciprocating bar of the machine, its blade at the moment of taking the successive loop of the thread of the looper hook obstructing the passage of the latter, which results in their mechanical engagement and relative slipping requiring a considerable effort.
Furthermore, the tip of the needle eye at the end of the point of the blade obstructs the shedding of a loop of the thread of the looper hook. The runs of the loop of the thread of the looper hook, when being shed, extend at an angle relative to the tip of the needle eye, so that the loop is caught by the tip as if the latter were a hook. The runs of the loop are thus overextended, the timing of the loop-shedding is impaired, the stitch-forming is affected, and the looper mechanisms are subjected to an additional load.